This invention relates to an engine control method and engine control structure for a small vehicle and more particularly to an improved engine control that prevents unwanted vehicle performance such as wheel slippage or undue lifting of a vehicle wheel from the ground without adversely affecting performance.
In certain types of small vehicles such as motorcycles or motor scooters, there has been a problem in that if rapid acceleration occurs, either or both of two undesirable phenomena result. One is slippage of the rear wheel that results in the loss of traction for driving and the other is a condition where there acceleration is so rapid that the front wheel actually may lift from the ground causing a phenomenon referred as to performing a xe2x80x9cwheeliexe2x80x9d. Neither result is desirable.
It has been proposed, therefore, to provide an arrangement wherein the engine output is reduced under situations where these conditions are likely to occur. The engine power reduction may be accomplished in a variety of manners such as changing ignition timing, skipping ignition timing or others.
Normally this condition is determined by sensing when the acceleration of the vehicle or a component of the vehicle exceeds a predetermined value. If this value is exceeded, then the power is reduced and the condition avoided.
However, the prior art methods of accomplishing this result are based upon acceleration alone and power reduction may occur even though it is not necessary to produce the aforenoted affects. For example, if the vehicle is being accelerated in downhill travel, the acceleration necessary to cause wheel slippage or a wheelie to occur is considerably different than that when traveling on an uphill condition.
FIG. 1 is a graphical view showing how these prior art type of systems operate. The top curve of this (A) is the acceleration of the vehicle, which can either be in the form of acceleration of the rotational speed of a shaft of the vehicle as Nxe2x80x3 or the angular acceleration of the shaft indicated as xcfx89xe2x80x3.
If these accelerations exceed a predetermined value indicated at Nxe2x80x2o or xcfx89xe2x80x2o which occurs at the time t1 as shown in the graphs, then the engine speed or power output is reduced, for example by delaying the spark timing from a normal angle xcex2 O to a retarded angle xcex21. This retardation is normally held for a predetermined time period as indicated by the timing period xcex94 t.
Then the spark timing is returned to its normal timing either abruptly or gradually as shown in the timing curve B of this figure. The acceleration of the shaft again increases but does not reach the level prior to application of control for some time. However, as noted above, it is found that this results in unnecessary and at times detrimental loss of engine performance.
In addition to the condition noted above i.e. traveling on a grade, it has been discovered that other conditions may occur when the acceleration exceeds the predetermined degree of acceleration used in the prior art methodology but the aforenoted undesirable driving conditions do not result. For example, if the throttle is moved relatively slowly, as may occur when traveling downhill, the acceleration rate can still exceed that preset and power is unnecessarily reduced with the prior art methods and systems. Also, if the throttle grip is moved rapidly from the closed position to a partially opened position or quickly from the partially opened position to a fully opened position, the acceleration rate of the prior art methods may be exceeded but the running conditions are such that the undesirable vehicle conditions will not occur. Thus, performance is inadvertently and unnecessarily decreased with the prior art methods and systems.
It is, therefore, a principal object to this invention to provide an improved method for engine control for a vehicle that will reduce the power but only at times when undesirable vehicle conditions will occur.
It is a further object to this invention to provide an engine control arrangement and method wherein the power is reduced only under certain specific conditions when it will be certain that undesirable vehicle running conditions may occur.
A first feature of this invention is adapted to be embodied in an engine control method for a vehicle in which rotation of an internal combustion engine shaft is transmitted to a driven wheel through a transmission. The method comprises the steps of detecting variations in the rotational state of the shaft during engine acceleration, determining if the degree of rotational variation is excessive, and restricting engine output if the rotational state of the shaft is excessive.
Another feature of the invention is adapted to be embodied in a vehicle engine control. The vehicle has an internal combustion engine, a driven wheel and a transmission for driving the driven wheel from a shaft of the internal combustion engine. An engine control detects variations in the rotational state of the shaft during engine acceleration. If the engine control determines the degree of rotational variation is excessive, the engine output is reduced.